Liquid cooled flash-producing apparatus



H. E. EDGERTON LIQUID COOLE'D FLASH-PRODUCING APPARATUS March 10, 1959 Filed June 28, 1955 0 N W; E Y u WDWN I. m M E A m I 2,877,341 Patented Mar. 10, 1959 Free LIQUID COOLED FLASH-PRODUCING APPARATUS Harold E. Edgerton, Belmont, Mass.

Application June 28, 1955, Serial No. 518,571

The present invention relates to light-producing apparatus and methods of operating the same; and, more particularly, to electronic flash-tube apparatus of the type suitable for stroboscopic and flash-photographic applications and the like.

One of the problems attendant upon the use of various light sources, such as lamps and arcs of various types, is the high temperature that develops during prolonged operation of the light sources. Air blowers and the like have been employed for cooling purposes, but they are, of course, bulky and inconvenient. In the case of mercury arcs and other continuously operated lamps, as a further example, the are or lamp has been provided with a jacket containing a liquid, such as water, for cooling the arc or lamp. It has also been proposed, as another illustration, to insert gaseous-conduction lamps in electrolytic solutions which not only serve as a cooling medium, but serve, also, as a light-ray and color filter or absorber.

While such techniques are at least'somewhat satisfactory for these continuously operated lamps and ares, they are entirely unsuited for high-voltage repetitively-flashed electronic gaseous-discharge cold-cathode flash-tubes of the type utilized in stroboscopes and flash photography.

Such flash-tubes are described, for example, in my United States Letters Patent 2,358,796, issued September 26, 1944, and also, in United States Letters Patent 2,492,142, issued December 27, 1949, to Kenneth I. Germeshausen. The high-voltage flash-tube operation frequentlyrequires the use of an external trigger electrode and, in addition, results in such high envelope temperatures that the envelope becomes conducting and short-circuits the high-voltage developed between the internal principal electrodes of the flash-tube. The use of conducting water or electrolytic media, as before described, would therefore entirely short-circuit the operation of such flash-tubes. In connection with such flash-tubes, therefore, attempts have been made either to utilize air-blowingicoolers or to employ external gas-filled jackets and the like for carrying away the heat generated by the high-voltage flashes. Unfortunately, however, neither of these proposals, nor otherattempts at solution of this problem, has been satisfactory. Flash-tubes must often be used in stroboscopic and flash-photographic applications, for example, where air-blowers are not only impractical, but prohibitive in view of their size and/or cost. Gas-filled external jackets, moreover, do not have, and inherently can not in practice produce, suflicient heat capacity satisfactorily to cool repetitively flashed high-voltage flash-tubes.

An object of the present invention, therefore, is to provide a new and improved light-producing apparatus and a novel method of operating thesame that shall not be subject to anyof the above-described disadvantages, but, on the contrary, shall particularly provide for the practical cooling of high-voltage repetitively discharged flashtubes.

A further object is to provide a new and improved flash-tube apparatus. In accordance with the present invention, this result is attained through the enclosure and supporting of the flash-tube in a transparent envelope filled with a transparent cooling dielectric liquid. Preferred details are hereinafter set forth.

Still an additional object is to render the flash-tube and its electrode and lead-conductor assemblies easily applicable to and removable from the dielectric-liquid-filled envelope. This is further to be contrasted with the fixed nature and special multiple electrode and lead-conductor seals and jackets required in prior-art systems.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be explained in connection with the accompanying drawings the single figure of which is a perspective view, partly broken away to illustrate details of construction, of a preferred embodiment of the invention.

A tubular substantially linear cold-cathode gaseousdisoharge flash-tube 1 is shown provided with internal anode and cathode principal electrodes 3 and 5 disposed in enlarged terminal portions 7 and 9 of the tube envelope 1. The space between the electrodes 3 and 5 is of reduced cross-section and constitutes the region 11 in which a highvoltage gaseous-discharge occurs between the principal electrodes 3 and 5 to produce a high-intensity flash of light. An exposed external trigger electrode 13 is shown wound about this region 11. The flash-tube 1 may, for example, be of the type FT-427 manufactured by the General Electric Company, or the type FT-2l8, or of any other desired type including those types described in the said Letters Patent. The envelope 1 may be of glass or fused quartz, as an illustration.

Since it is desired to convert as much of the energy stored prior to the discharge between the anode 3 and the cathode 5 into visible light when the discharge is triggered, it is important that as much of the gas in the region 11 be ionized by the discharge as is possible. In the tube 1, accordingly, the gas-ionized discharge between the electrodes 3 and 5 extends outward to the walls of the reduced-dimension region 11 of the envelope 1 and subjects those walls to extremely high instantaneous temperatures. As the tube 1 is repetitively periodically flashed in air, or other gaseous surroundings, either as a stroboscopic light source or for flash-photographic purposes and the like, the region 11 of the envelope 1 heats more rapidly than the heat can be carried away from the envelope 1. Not" only does the flash-tube thereupon start to miss in its periodic flashing as a result of accumulated heat in the gaseous medium within the envelope 1, but the walls 11 t of the tube approach temperatures in excess of 500 degrees centigrade at which the glass or similar envelope becomes reasonably conductive, as before mentioned, thus destroying the satisfactory operation of the flash-tube. Since the before-described cooling techniques have not proved satisfactory for the particular problems involved in the use of such flash-tubes, it has been necessary, in the art, to operate the flash-tubes at appreciably reduced efficiency in order that the temperature of the tube walls may remain relatively low even when the flash-lamp is flashed at high repetition rates.

By immersing the flash-tube 1 together with its electrode-and-lead-conductor assembly in a transparent tubular housing 15, shown as a substantially cylindrical glass tubing closed over at the free or left-hand end and filled with an appropriate transparent dielectric liquid.

medium 17, the problem of flash-tube overheating has become solved and the flash-tube can be operated, even for rapid-repetition-rate stoboscopic purposes, with full high-voltage and full efiiciency. The present invention also permits flash-tubes to be flashed continually for the first time in optical systems such as studio photo graphic apparatus, microscope photographic apparatus, and line-source instrumentation apparatus, in which it is desirable to use the same light source both for focusing and for taking the high-intensity flash photograph.

There are several important and highly restrictive requirements, however, upon the dielectric medium 17. As before stated, it must be transparent and must not absorb appreciable light energy. Since the electrode lead-conductors 19 and 21, connected respectively to the anode 3 and the cathode 5, extend exposed through end seals in the respective terminal portions 7 and 9 of the flash-tube 1, and since the trigger electrode 13 is also exposed, the medium 17 can not be of Water or electrolyte, as before mentioned, but must have high-voltage dielectric or insulating properties. Not only must the medium 17 be transparent as well as possessing a high-voltage dielectric characteristic, however, but it must remain transparent, with substantially no significant decomposition, color change, or alteration of light-absorption or refractive characteristics, and it must remain of highinsulating characteristic even when it becomes heated through the operation of the flash-tube 1. More than this, however, the medium 1 must have a relatively high heat capacity and it must also be of sufficient dimensions or volume to permit appreciable heat conduction. When such a medium 17 is employed, it has been found that as the region 11 of the flash-tube 1 heats up, the density of the medium 17 immediately adjacent the region 11 will decrease, driving the medium outward in a selfpumping or circulating action that carries the heat away from the tube 1.

Among the liquid media 17 that have been found satisfactory in varying degrees for this purpose are heavy mineral oil, ethylene glycol and carbon tetrachloride. While in some applications, slight discoloration may occur if a quartz envelope 1 is employed, improved results may be obtained through the use of a glass envelope 1 that will not pass the ultra-violet radiation of the light flash into the medium 17 and will not, therefore, subject the medium to the chemical changes that are often produced by ultra-violet rays.

In order to obtain the principal benefits of the present invention, the volume of the dielectric liquid medium 17 should be sufficient that the amount of heat absorbed by the medium, without elevation to a temperature of the order of 500 degrees centigrade, will be at least about ten or more times the amount of heat absorbed in the flash-tube 1. If the flash-tube 1 were normally operated in air as a 7-to-l0 watt device, as an example, the invention is most useful when the volume of the dielectric liquid medium 17 is suflicient to absorb at least about 70 to 100 watts of energy without reaching such extreme temperatures. With a flash-tube 1 of about 20 to 30 cubic cantimeters of volume, a greater volume of, for example, a heavy mineral oil medium 17 in the housing 15 of the order of about one-half a liter has been found successfully to accomplish this result.

The dielectric liquid in contact with the external wall of the flashtube 1 is effective in preventing the wall temperature from rising to high values. Once the liquid next to the wall becomes heated, it rises and thus allows fresh cool liquid to continuously contact the hot surface. Eventually the boiling condition is reached Where a sequence of bubbles is formed at the surface of the flashtube. A small bubble of air 16 is sometimes left in the liquid container to prevent the buildup of pressure to abnormal values that might cause the outside container to break.

Returning to the details of construction of the illustrated embodiment of the invention, the terminal portions 7 and 9 of the flash-tube 1 are shown supported substantially parallel to but displaced from the axis of t 4 the cylindrical housing 15 by the lower clamps of the respective pairs of clamps 23 and 25. A hollow tube 27, as of glass, is similarly symmetrically disposed off the axis of the housing 15 within the upper clamps of the pairs of clamps 23 and 25 to give balance to the mounting structure and to serve, also, as a conduit for the lead-conductor 29 associated with the cathode electrode 5 and its lead-connection 21. The ends of the upper and lower clamps of the pairs of clamps 23 and 25 are shown outwardly bowed, as at 31 and 33, to provide for a spring-fit of the assembly 127 within the housing 15 that prevents movement of the flashtube, and the rearward or right-hand pairs of clamps 23 are shown intermediately supported by a rod 35 upon an end plate 37 disposed at the open end of the housing 15. The cathode conductor 29 passes through the end plate 37 at the sealed outlet 38 and is connected by a further conductor 29' passing through an external preferably cylindrical housing 39 to the left-hand terminal of a high-voltage flash capacitor or capacitors C. A similar anode conductor 41, connected to the anode 3 by the lead-connector 19, passes through an outlet 43 in the end plate 37, similar to the outlet 38, and connects by a conductor 41' to the bottom terminal of a triggervoltage pulse transformer, schematically shown at T, disposed within the housing 39. The conductor 41' connects, in turn, with the right-hand terminal of the capacitor or capacitors C. The external trigger electrode 13 is connected by a similar conductor 45 through an outlet 47 in the end plate 37 to a further conductor 45' that connects with the upper terminal of the secondary or step-up winding S of the trigger transformer T. In operation, when the switch 49 is closed, a battery or other source of high-voltage energy B will charge the capacitor or capacitors C through the charging impedance R. Conductors 41 and 29' apply this high voltage between the anode 3 and cathode 5 of the flash-tube 1, but the voltage is not enough to break down the gas in the tube 1. A trigger device 51 of any desired type, such as a single or repetitive pulse-producing circuit, applies a trigger voltage pulse to conductors 41' and 53 and thus to the primary winding P of the trigger transformer T. A high-voltage trigger pulse results in the secondary winding S which is applied by conductors 45', 45 and 41', 41 between the trigger electrode 13 and the electrode 3 to trigger the brake-down of the'gas in the tube 1 and thereby to permit the high voltage of the capacitor or capacitors C to discharge between the electrodes 3 and 5, producing a high-intensity flash of light along the region 11.

The rearward housing 39 is shown provided with terminal flanges 52 and 55 for mounting the assembled apparatus. A gasketed mounting plate 57 may also be employed to secure and seal the housing 15 to the terminal flange 52 by clamping the preferably flared right-hand end of the housing 15. A cylindrical reflector 63 may be employed for focusing the light produced by the linear region 11 of the flash-tube 1, where directionality of the light flashes is desired. The reflector 63 is positioned adjacent preferably an external portion of the housing 15 where the flashatube 1, offset from the housing axis, as before described, is substantially along the line focus of the reflector. Support for the reflector 63 may be provided by external mounting brackets 59 and 61. Through this mounting construction, moreover, the flashtube 1 may be easily inserted or removed from the housing 15 and no special electorde seals, jackets or insulators are required. This mounting structure has been found particularly useful in the employment of this apparatus exterior to a ship for such purposes as, for example, underwater high-intensity stroboscopic observation of propeller operation.

As an illustration of a practical system useful for 'such purposes, the flash-tube 1, as of the FT-427 type previously mentioned, may be mounted within an oilfilled Pyrex glass tube 15 about three inches in inner diameter. -Theactive. length 11:.of-the flash-tube 11 may be about'eleven inches. The flashing rate provided by the trigger device 51.for propeller observations maybe about 5 flashes per second. The capacitors C may be charged to about 4200 volts with a 200 Watt-second input torthe flash-tube. One kilowatt output operation has been thus achieved over indefinite periods of time. The FT-218-type flash-tube, as another example, has also been successfully operated in accordance with the present invention over extended periods of time with as much as 100 watts input.

It is to be understood that flash-tubes of other configurations than that illustrated, such as are described, for example, in the said Letters Patent, as Well as housings and mountings of other shapes and types may also be employed. The liquid may, if desired, be circulated or the housing may be provided with external cooling paths therefor, not shown. Other types of flash-producing circuits, such as those described in the said Letters Patent, may, of course, also be utilized, with or without an external trigger electrode.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid, a gaseous-discharge flash-tube having exposed electrode lead connections, and means for supporting the complete flash-tube with the exposed electrode lead connections within the dielectric liquid in the housing.

2. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid, a gaseous-discharge flash-tube having an exposed trigger electrode and exposed principal-electrode lead connections, and means for supporting the complete flash-tube with the exposed trigger electrode and exposed principal-electrode lead connections within the dielectric liquid in the housing.

3. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing filled with a light-transparent dielectric liquid but containing a gas bubble, a gaseous-discharge flash-tube having exposed electrode lead connections, and means for supporting the complete flash-tube with the exposed electrode lead con nections within the dielectric liquid in the housing, the volume of the dielectric liquid in the housing being greater than the gaseous-discharge volume of the flash-tube.

4. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid, a gaseous-discharge flash-tube having exposed electrode lead connections, and means for supporting the complete flash-tube with the exposed electrode lead connections within the dielectric liquid in the housing, the volume of the dielectric liquid being suflicient to increase the heat capacity of the apparatus at least substantially ten times that of the said flash-tube disposed in air.

5. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid selected from the group consisting of light-transparent mineral oil, ethylene glycol and carbon tetrachloride, a gaseous-discharge flashtube having exposed electrode lead connections, and means for supporting the complete flash-tube with the exposed electrode lead connections within the dielectric liquid in the housing.

6. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid, at gaseous-discharge flash-tube having exposed electrode lead connections, means for supporting the complete flash-tube with the exposed electrode tleadxeonnections .nwithinpthe dielectric liquid in the housing, means @idisposed external to the housing forsupplying yoltage of predetermined value to the said electrode 'lead' connections, and a reflector mounted adjacent aportion' ofthe housing, the dielectric liquid remaining an effective dielectric for said voltage value.

7. Flash-producing apparatus comprising a completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid and closed at one end, an end seal disposed at the other end, a gaseous-discharge flash-tube having electrodes and associated exposed electrode leads, means for supporting the complete flash-tube within the dielectric liquid in the housing with the exposed electrode leads in contact with the dielectric liquid, and 1 means for establishing electrical connections with the flashtube electrode leads through the end seal to flash the flashtube.

8. Flash-producing apparatus comprising a substantially cylindrical completely liquid-sealed closed light-transparent housing containing a light-transparent dielectric liquid and closed at one end, an end seal disposed at the other end, a substantially linear tubular gaseous-discharge flash-tube having electrodes and associated exposed elec trode leads, clamping means for mounting the flash-tube substantially parallel to the axis of the housing completely within the dielectric liquid in the housing with the exposed electrode leads in contact with the dielectric liquid, an electric flash-producing circuit mounted external to the housing, and means for establishing electrical connections between the circuit and the flash-tube electrode leads through the end seal to flash the flash-tube.

9. Flash-producing apparatus comprising a substantially cylindrical light-transparent housing containing a lighttransparent dielectric liquid and closed at one end, an end seal disposed at the other end, a substantially linear tubular gaseous-discharge flash-tube having electrode means and associated exposed electrode leads, clamping means for mounting the flash-tube substantially parallel to though displaced from the axis of the housing completely within the dielectric liquid in the housing with the exposed electrode leads in contact with the dielectric liquid, an electric flash-producing circuit mounted external to the housing, means for establishing electrical connections between the circuit and the flash-tube electrode leads through the end seal to flash the flash-tube, and a cylindrical reflector mounted adjacent a portion of the housing.

10. Flash-producing apparatus as claimed in claim 9 and in which the clamping means supports also a tubular member, the member and the flash-tube being symmetrically disposed with respect to the housing and the member being adapted to receive and support an electrical lead conductor.

11. Illumination-producing apparatus comprising a completely liquid-sealed closed light-transparent housing filled with a light-transparent dielectric liquid but containing a gas bubble, a gaseous discharge flash tube having a predetermined volume within which illumination is produced and exposed electrical lead connection, means for supporting the flash tube within the dielectric liquid in the housing with the electrical lead connections in contact with the dielectric liquid, the volume of the dielectric liquid in the housing being greater than the said predetermined volume.

12. Illumination-producing apparatus comprising a completely liquid-sealed closed light-transparent housing filled with a light-transparent dielectric liquid but containing a gas bubble, a gaseous discharge flash tube having exposed electrical lead connections, and means for supporting the flash tube within the dielectric liquid in the housing with the electrical lead connections in contact with the dielectric liquid, the volume of the dielectric liquid being sufiicient to increase the heat capacity of References Cited in the file of this patent UNITED STATES PATENTS De Forest July 11, 1916 8 Coolidge Mar. 7, 1922 Brandt July 4, 1939 Van Alphen Mar. 26, 1940 B01 Feb. 23, 1943 Edgerton Sept. 26, 1944 Casellini et a1. Dec. 27, 1949 

